Induction motor



Sept. 22, 1925.

s. R. BERGMAN INDUCTION MOTOR Fiied Nov.

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Patented Sept. 22, 1925..

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rasant SVEN' R. BERGMAN, OF NAHANT, MASSACHUSETTS, ASSIGNOR T0 GENERAL EIEGTRC COMPANY, A. CORPORATION OF NEW YORK.

INDUCTION MOTOR.

Application led November 29, 1924. Serial No. ?52,91l.

To all lvito/m t may concern:

Be it known that l, SVEN R. BERGMAN, a subject of the King of Sweden, residing at Nahant, in the county of Essex, State of Massachusetts, have invented certain new and useful Improvements in Induction Motors, Qiwhich the following is a specitcation.

My invention relates to induction motors and particularly to such motors of the squirrel cage type'.

It is well known that in order that an induction motor should start under load without 'an excessive current flow, it is necessary that. the secondary circuit shall possess 4a high resistance,- and on the other hand, that when the motor is up to speed vthe resistance and the reactance of the' secondary circuit should be low in order to secure eihcient operation.

It has been proposed heretofore to provide the secondary member of an induction motor with two squirrel cage windings, one of high resistance and low reactance and the other of low resistance and high. reactance. When'starting with such an arrangement, the frequency of the secondary currents is high and the high resistance windings will carry the greater part of the load, but when the motor is up to speed, the frequency of the secondary currents is low and the low resistance winding will carry the load.

My invention relates to induction'motcrs of the above described type and has for its obj ect, a novel construction and arrangement of parts, whereby such motors have a better starting torque, and a higher eliiciency and very slightly lower power factor at normal speeds, than ordinary squirrel cage induction motors, and better characteristics than double squirrel cage induction motors as heretofore constructed.

To this end, my invention consists in providing the rotor with conducting elements placed in alternately deep and shallow slots forming teeth therebetween of substantially uniform cross section, the conducting elements in the shallow slots and the conducting elements in the top of the deep slots being connected together to form a high resistance, low reactance squirrel cage winding and the conducting elements in the bottom of the deep slots being connected togetherA to form a low resistance high reactance' squirrel cage winding.

By making the teeth of substantially uniform cross-section between the deep and shallow slots, l obtain uniform'density in the rotor teeth. In this way the magnetic material is most emciently utilized. Furthermore with my construction, both Windings are of comparatively low reactance because the conductors in the deep slots have little leakage ux crossing them. Nevertheless the winding formed of the conductors in the shallow slots and the conducting elements in the top of the deep slots, which is of high resistance, is of somewhat lower reactance than the other winding because practically no flux crosses it. The winding formed of the conducting elements in the bottom of the deep slots, however, since it is of large cross-section, is of low resistance and it has higher reactance than the other winding, since, when the motor is start-ing, flux will lealr across the deep slots above the conducting elements of large cross section and little ux will pass under these slots. A motor provided with two such windings, therefore, has a better startingtorque and a higher elhciency and only slightly lower power factor at normal speed than an ordinary squirrel cage motor and better characteristics in all.. respects than double squirrel cage motors as heretofore constructed.

For a better understanding of my invention and other features'of novelty, reference may be had to the following specification taken in connection with the accompanying drawings, in which Fig. l shows an end view, partly in section, of a portion of the rotor of an induction motor arranged in. accordance with my invention, and Fig. 2 shows a crosssectional view of the portion of the rotory of Fig. l.

In the drawing, 1 represents the rotor core which is built up of laminations mounted on a spider 2, the spider being mounted on a shaft 3 in the usual manner. The rotor core is provided with alternately dee slots 4 and shallow slots 5. The shallow s ots 5 have a single conducting clement 6 therein, whereas the deep slots 4 have two conducting elements therein, one, 7, in the top thereofand the other, 8, in the. bottom thereof. All of the conducting elements in all the slots are shown as being connected together at the ends by short-circuiting'orend rings 9,. one at each lend of the rotor core,a The conducting elements 6 in the shallow slots and the conducting elements 7 in the top of the deep slots are connected together to 'form a high resistance, low reactance squirrel cage winding and the conducting elements 8 in the bottom of the deep slots are connected together 'to form a low resistance, high reactance squirrel cage winding. As will be seen from the drawing, the teeth l0 formed between the deep and shallow slots are substantially uniform in cross-section, whereby uniform magnetic density in the teeth is obtained. nthe particular arrangement shown in the drawing, the deep slots are narrower in that portion thereof near the periphery ot the rotor than the shallow slots, and thereby there is provided a small air gap across which the 'tluX will pass when the inotor is starting, little flux passing underneath the deep slots thus the winding composed of the conducting elements in the bottom ot the deep slots has a higher reactance than the winding composed ot' the conducting elements in the top of the deep slots and the conductors' in the shallow slots. The teeth are made uni-form in cross-section by providing the narrow portion ot the deep slots with substantially parallel sides, which are substantially parallel with the sides of the shallow slots, and the cross-section of each of the teeth between the bottom of said deep slots is substantially double that ot the crosssection ot a tooth between the portion of a deep slot near the periphery of the rotor and a shallow slot, whereby the. magnetic density throughout the depth of the rotor teeth is substantially uniform. The bottom portions of the dee-p slots, that is, the portions of these slots further away from the periphery of the rotor, are wider than the top portions.

In practice, I find it advantageous to cast the conductor portions 6, 7 and 8 and the end rings 9 as a unitary structure. This may be done in any suitable manner but I prefer to employ the method is illustrated in the Reist & Maxwell Patent No. 1,100,009, dated July Ll, 1916. By casting the windings, the conducting elements 7 and 8 in each ot the deep slots are -formed as a single conductor and completely fills such slot.

lVhat I claim as new and desire to secure by Letters Patent of the United States, is

l. In an induction motor a rotor provided with alternately deep and shallow slots forming teeth therebetween, conducting elements in said slots, said conducting elements in said shallow slots and said conducting elements in the top of said deep slots being connected together to form a high resistance low reaetan'ce squirrel cage winding, said conducting elements in the bottom ot said deep slots being connected together to form a low resistance high reactance squirrel cage winding, said teeth being of substantially uniform cross-section between said deep and shallow slots whereby the magnetic density in said teeth is uniform.

Q. ln an induction motor a rotor provided with alternately deep and shallow slots forming teeth therebetween, a single conducting element in said shallow slots, a plurality of conducting elements in said deep slots, one in the top ot' said deep slots and one in the bottoni thereof, said conducting elements in said shallow slots and said conducting elements in the top ot said deep slots being connected 'together to torni a high resistance low react-ance squirrel cage winding, said conducting elements in the bottoni ot said deep slots being connected together to form a low resistance high reactanee squirrel cage winding, said teeth being of substantially unilorm cross-section between said deep and shallow slots whereby the magnetic density in said teeth is uniform.

3. In an induction motor a rotor provided with alternately deep and shallow slots forming teeth therebetween, conductors substantially tilling said slots, said conductors in said deep slots haring a plurality ot conducting elements, one in the top ot said slots and one in the bottom ol' said slots, said conductors in said shallow slots andsaid conducting elements in the top ot said deep slots being connected together to torni a high resistance low reactance squirrel cage winding, said conducting elements in the bottom of said deep slots being connected to gether to form a low resistance high reactance squirrel cage winding, said teeth being ot' substantially uniform cross-section between said deep and shallow slots whereby the magnetic density in said teeth is substantially uniform.

4t. In an induction motor a rotor provided with alternately deep and shallow slot-1 forming teeth therebetween, a conductor in each ot' said slots substantially. tilting thtI same, and rings connecting all ot said conductors together so as to form a plurality ol' squirrel cage windings, one ot' said squirrel cage windings comprising the conductors in 'said shallow slots and the conducting elements in the top of said deep slots and the other of 4said squirrel cage windings coniA prising the conductor elements in the bottom ot said deep slots, said teeth being ol' substantially uniform crosssection between said deep and shallow slots whereby the magnetic density in said teeth is uniform. l

5. In an induction motor a rotor provided with alternately deep and shallow slots lorining teeth therebetween, said deep slots being narrow in that portion thereof near the periphery ot the rotor and having substantially parallel sides in this portion thereof, the portions of saidslots 'further away from said peripheral being wider than the first mentioned portions ot the slots, a conductor in each ot said slots substantiallil ltlil llo ly filling the same, andY rings connectin all of said conductors together so as to orm a plurality of squirrel cagel windings, one of,said squirrel cage windings .comprising the conductors in -said lshallow slots and the conducting elements in the top of said deep slots and the other'of said squirrel cage-windings comprising the conductor elements in the bottom of said deep slots, said winding, said teeth being of substantially uniform cross-section between 'said deep and shallow vslots and the cross-sectionof each of the teeth 'between the ,bottom of said deep slots being substantially double that of the cross-section of a tooth between the top part of a deep slot and a shallow slot.

7. In an induction motor a rotor provided withI alternately deep and. shallow slots forming teeth therebetween, conductors substantially filling said slots, said conductors in vsaid deep slots having a plurality of conducting elements, one in the top of said slots and one in the bottom of said slots, said conductors in said shallow slots and said conducting elements in the top of said deep slots being connected together to form a high resistance low reactance squirrel cage winding, said conductin elements in the bottom ofsaid deep slots eing connected together to forma low resistance 'high reac tancesquirrel cage winding, said teeth being of substantially uniform cross-section between said deep and shallow slots andthe cross-section of each of the teeth between the bottom of said deep slots being substantiall double .that of the cross-section of a toot between the top part of a deep slot and a shallow slot.

8. In an induction motor, a rotor provided with 'alternately deep and Shallow slots forming 'teeth therebetween, said deep slots being narrower in those portions thereof near the periphery of the rotor than the shallow slots, sald portions of the deep slots having substantially 'parallel sides, the. portions of said deep slots further away from said peripheral being wider than the first mentioned -portions of said dee slots, ay conductor in each of said slots substantially filling the same, and rings connecting all said conductors together so as to form a plurality of squirrel cage windings, one of lsaid squirrel cage windings comprism the conductors in said Ishallow slots an the conducting elements inthe to of said deep slots andv the other of sai squirrel cage windings comprising the conductor elements inthe bottom of said deep slots, said teeth being of substantially uniform cross-section between said deep and shallow slots whereby the magnetic density in said teeth `is uniform.

9. In an induction motor, a rotor` provided with alternatel deepand shallow slots forming teeth there ietween, said deep slots being narrower in those portions thereof near the periphery of the rotor than the shallow slots, said portions of the deep slots having substantially arallel sides, the portions of said slots further away from said peripheral being wider than the first mentioned portions of said deep slots, a conductor in each of said slots substantially filling the same, and rings connecting'all of said conductors together so as to form a plurality of squirrel cage windings, one of said squirrel cage windings comprising the conductors in said shallow slots and the conducting elements in the top of said deep slots and the other of said squirrel cage windings comprising the conductor elements in the bottom of said deep'slots, said teeth being of substantially uniform cross-section'between said deep and shallow slots and the cross-section of each,

of the teeth between the bottom of said deep slots being substantially double that of the cross-section of a tooth between the ortion of a deep slot near the periphery o the rotor and a shallow slot.

In witness whereof, I have hereunto set my hand this 26th day of November 1924.

SVEN R. BERGMAN. 

